Cement slurries, cured cement and methods of making and use of these

ABSTRACT

Cement slurries, cured cements, and methods of making cured cement and methods of using cement slurries are provided. The cement slurries have, among other attributes, improved elasticity and self-healing properties and may be used, for instance, in the oil and gas drilling industry. The cement slurry comprises water, a cement precursor material, and a block copolymer composition. The block copolymer composition has at least one copolymer backbone, with each copolymer backbone comprising at least two hard segments. Furthermore, a soft segment is disposed between the at least two hard segments. The copolymer backbone has at least one anhydride group grafted onto the soft segment, and the anhydride group is crosslinked by an aminosilane crosslinker.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 16/426,092 filed May 30, 2019, the entire disclosure of whichis hereby incorporated herein by reference.

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to cementslurries and methods of making and using cement slurries and to curedcements and methods of making cured cement.

BACKGROUND

Cement slurries are used in the oil and gas industries, such as forcementing in oil and gas wells. Primary, remedial, squeeze, and plugcementing techniques can be used, for instance, to place cement sheathsin an annulus between casing and well formations, for well repairs, wellstability, or for well abandonment (sealing an old well to eliminatesafety hazards). These cement slurries must be able to consistentlyperform over a wide range of temperatures and conditions as cement setin an oil and gas well may be vulnerable to cyclic stresses imposed bypressure and temperature fluctuations. A brittle cement may crack andbreak under these stresses, reducing the integrity of the wellbore.

SUMMARY

Adding elastomers to cement slurry can be vital to the elasticity,strength, and performance properties of the cured cement composition.However, conventional aqueous latex fluids contain limited amounts ofelastomer additive, leading to too little elastomer throughout the setcement, as adding too much aqueous fluid can lead to an inability forthe cement to set. Furthermore, too little elastomer leads to curedcements without self-healing capabilities.

Accordingly, there is an ongoing need for cement slurries that areresistant to cyclic stresses, elastic in nature, and exhibitself-healing capabilities. Furthermore, cured cements that are elasticprevent cracking and breaking under cyclic stresses. The presentembodiments address these needs by providing cement slurries and methodsof making and using cement slurries that include a block copolymercomposition.

In one embodiment, a cement slurry is provided that comprises water, acement precursor material, and a block copolymer composition. The blockcopolymer composition has at least one copolymer backbone, with eachcopolymer backbone comprising at least two hard segments. Furthermore, asoft segment is disposed between the at least two hard segments. Thecopolymer backbone has at least one anhydride group grafted onto thesoft segment, and the copolymer backbone is crosslinked by anaminosilane crosslinker.

Additional features and advantages of the described embodiments will beset forth in the detailed description which follows, and in part will bereadily apparent to those skilled in the art from that description orrecognized by practicing the described embodiments, including thedetailed description which follows as well as the claims.

DETAILED DESCRIPTION

As used throughout this disclosure, the term “block copolymer” refers toa polymer having at least two compositionally distinct subunits (A andB) derived from different monomer species. The at least twocompositionally distinct subunits are covalently bonded to one anotherand linearly oriented.

As used throughout this disclosure, the term “polymer backbone” or“copolymer backbone,” which may also be called “the main chain,” is thelinearly-oriented polymeric chain to which all side chains or moietiesare attached or grafted to.

As used throughout this disclosure, the term “grafting” refers to areaction in which one or more compositions are connected to the mainchain or polymer backbone as a side chain in which the graftedcomposition is compositionally different than the polymer backbone.

As used throughout this disclosure, the term “crosslinking” refers tothe covalent bonding of a first polymeric chain with a second polymericchain using a crosslinking agent.

As used throughout this disclosure, the terms “soft segment” and “hardsegment” refer to relative block portions (or blocks) of the polymerchain. The soft segment is the block portion of the polymer chain thatif it was in a pure homopolymer form would have a reduced glasstransition temperature and would have lesser rigidity relative to thatof a similar pure homopolymer form of the block hard segment.

As used throughout this disclosure, the term “cement slurry” refers to acomposition comprising a cement precursor that is mixed with at leastwater to form cement. The cement slurry may contain calcined alumina(Al₂O₃), silica (SiO₂), calcium oxide (CaO, also known as lime), ironoxide (FeO), magnesium oxide (MgO), clay, sand, gravel, and mixtures ofthese.

As used throughout this disclosure, “curing” refers to providingadequate moisture, temperature and time to allow the concrete to achievethe desired properties (such as hardness) for its intended use throughone or more reactions between the water and the cement precursormaterial.

As used throughout this disclosure, “drying” refers to merely allowingthe cement to achieve a moisture condition appropriate for its intendeduse, which may only involve physical state changes as opposed tochemical reactions.

As used throughout this disclosure, the term “retarder” refers to achemical agent used to increase the thickening time of cement slurriesto enable proper placement of the cement slurry within the wellbore. Theneed for cement retardation increases with depth due to the greater timerequired to complete the cementing operation and the effect of increasedtemperature on the cement-setting process.

As used throughout this disclosure, the term “subsurface formation”refers to a body of rock that is sufficiently distinctive and continuousfrom the surrounding rock bodies that the body of rock can be mapped asa distinct entity. A subsurface formation is, therefore, sufficientlyhomogenous to form a single identifiable unit containing similarrheological properties throughout the subsurface formation, including,but not limited to, porosity and permeability. A subsurface formation isthe fundamental unit of lithostratigraphy.

As used throughout this disclosure, the term “thickening time” refers toa measurement of the time during which a cement slurry remains in afluid state and is capable of being pumped. Thickening time is assessedunder downhole conditions using a pressurized consistometer that plotsthe viscosity of a slurry over time under the anticipated temperatureand pressure conditions. The end of the thickening time isconventionally about 50 or 70 Bearden units of consistency (Bc), adimensionless quantity with no direction conversion factor to morecommon units of viscosity. The Bearden units of consistency is measuredon a scale from 1 to 100 where difficult pumping begins at 50 Bc andcement is completely set at 100 Bc.

As used throughout this disclosure, the term “wellbore” refers to thedrilled hole or borehole, including the openhole or uncased portion ofthe well. Borehole may refer to the void space defined by the wellborewall, where the rock face that bounds the drilled hole defines theborehole.

Embodiments of the present disclosure relate to cement slurries andcured cements with elasticity and self-healing capabilities. Embodimentsof the present disclosure also relate to methods of producing and usingcement slurries, in some particular embodiments, for use in the oil andgas industries.

Oil and gas wells may be formed in subsurface formations. The wellboremay serve to connect natural resources, such as petrochemical products,to a ground level surface. In some embodiments, a wellbore may be formedin the subsurface formation, which may be formed by a drillingprocedure.

In some instances, a casing may be inserted into the wellbore. Thecasing may be a pipe which has a diameter less than that of thewellbore. Generally, the casing may be lowered into the wellbore suchthat the bottom of the casing reaches to a region near the bottom of thewellbore. In some embodiments, the casing may be cemented by inserting acement slurry into the annulus region between the outer edge of thecasing and the edge of the wellbore (the surface of the subsurfaceformation). The cement slurry may be inserted into the annular region bypumping the cement slurry into the interior portion of the casing, tothe bottom of the casing, around the bottom of the casing, into theannular region, or a combination of some or all of these. The cementslurry may displace the drilling fluid, pushing it to the top of thewell. In some embodiments, a spacer fluid may be used as a bufferbetween the cement slurry and the drilling fluid. The spacer fluiddisplaces and removes the drilling fluid before the cement slurry ispumped into the well to prevent contact between the drilling fluid andthe cement slurry. Following the insertion of an appropriate amount ofcement slurry into the interior region of the casing, in someembodiments, a displacement fluid may be utilized to push the cementslurry out of the interior region of the casing and into the annularregion. This displacement may cause the entirety of the spacer fluid anddrilling fluid to be removed from the annular region, out the top of thewellbore. The cement slurry may then be cured or otherwise allowed toharden.

To ensure the stability and safety of a well, it is important that thecured cement maintains integrity and isolates the wellbore from thesurrounding subsurface formations. If the cement cracks or degradesunder cyclic stresses, wellbore integrity and isolation may be lost,resulting in undesirable fluid communication between the wellbore andsurrounding subsurface formations. Not intending to be limited bytheory, this fluid communication may result in drilling fluid loss fromthe wellbore into the surrounding subsurface formation or in decreasedwellbore pressure, possibly leading to a well control event. Therefore,wellbore integrity and isolation are critical to effective productionand use of a wellbore.

The present disclosure provides cement slurries and cured cements whichmay have, among other attributes, elasticity and self-healingcapabilities to address these concerns. The cement slurry of the presentdisclosure includes water, a cement precursor material, and a blockcopolymer composition. The block copolymer composition has at least onecopolymer backbone, where each copolymer backbone further includes atleast two hard segments and a soft segment disposed between the two hardsegments. The copolymer backbone is further grafted with an anhydridegroup on the soft segment, and the anhydride group is crosslinked by anaminosilane crosslinker. In some embodiments, the aminosilanecrosslinker may include 3 (2 aminoethylaminopropyl)trimethoxysilane,3-aminopropyltriethoxysilane, or combinations of these.

The cement precursor material may be any suitable material which, whenmixed with water, can be cured into a cement. The cement precursormaterial may be a hydraulic or a non-hydraulic cement precursor. Ahydraulic cement precursor material refers to a mixture of limestone,clay and gypsum burned together under extreme temperatures that maybegin to harden instantly or within a few minutes while in contact withwater. A non-hydraulic cement precursor material refers to a mixture oflime, gypsum, plasters and oxychloride. A non-hydraulic cement precursormay take longer to harden or may require drying conditions for properstrengthening, but often is more economically feasible. A hydraulic ornon-hydraulic cement precursor material may be chosen based on thedesired application of the cement slurry of the present disclosure. Insome embodiments, the cement precursor material may be Portland cementprecursor, for example, Class G Portland Cement. Portland cementprecursor is a hydraulic cement precursor (cement precursor materialthat not only hardens by reacting with water but also forms awater-resistant product) produced by pulverizing clinkers, which containhydraulic calcium silicates and one or more of the forms of calciumsulfate as an inter-ground addition.

The cement precursor material may include calcium hydroxide, silicates,oxides, belite (Ca₂SiO₅), alite (Ca₃SiO₄), tricalcium aluminate(Ca₃Al₂O₆), tetracalcium aluminoferrite (Ca₄Al₂Fe₂O₁₀), brownmillerite(4CaO.Al₂O₃—Fe₂O₃), gypsum (CaSO₄.2H₂O), sodium oxide, potassium oxide,limestone, lime (calcium oxide), hexavalent chromium, trivalentchromium, calcium aluminate, silica sand, silica flour, hematite,manganese tetroxide, or combinations of these. The cement precursormaterial may include Portland cement, siliceous fly ash, calcareous flyash, slag cement, silica fume, quartz, or combinations of any of these.Silica flour is a finely ground crystalline silica with a molecularformula of SiO₂ and with a grain size ranging from 1 to 500 microns(μm), from 10 to 500 microns, from 10 to 100 microns, from 10 to 80microns, from 10 to 50 microns, from 10 to 20 microns, from 20 to 100microns, from 20 to 80 microns, from 20 to 50 microns, from 50 to 100microns, from 50 to 80 microns, or from 80 to 100 microns.

Water may be added to the cement precursor material to produce theslurry. The water may be distilled water, deionized water, or tap water.In some embodiments, the water may contain additives or contaminants.For instance, the water may include freshwater or seawater, natural orsynthetic brine, or salt water. In some embodiments, salt or otherorganic compounds may be incorporated into the water to control certainproperties of the water, and thus the cement slurry, such as density.Without being bound by any particular theory, increasing the saturationof water by increasing the salt concentration or the level of otherorganic compounds in the water may increase the density of the water,and thus, the cement slurry. Suitable salts may include, but are notlimited to, alkali metal chlorides, hydroxides, or carboxylates. In someembodiments, suitable salts may include sodium, calcium, cesium, zinc,aluminum, magnesium, potassium, strontium, silicon, lithium, chlorides,bromides, carbonates, iodides, chlorates, bromates, formates, nitrates,sulfates, phosphates, oxides, fluorides, vanadium, zirconium, orcombinations of these.

In some embodiments, the cement slurry may contain from 10 weightpercent (wt. %) to 70 wt. % by weight of cement precursor (BWOC) water.In some embodiments, the cement slurry may contain from 10 wt. % to 40wt. %, from 10 wt. % to 30 wt. %, from 10 wt. % to 20 wt. %, from 20 wt.% to 40 wt. %, from 25 wt. % to 35 wt. %, or from 20 wt. % to 30 wt. %BWOC water. The cement slurry may contain 30 wt. % BWOC water.

Along with the cement precursor material and water, the cement slurryincludes a block copolymer composition. The block copolymer compositionfunctions as an elastomer, which imparts elasticity and self-healingcapabilities to the cement. The block copolymer composition may melt ata specific temperature range, known as the melting temperature,resulting in a flowable medium. The block copolymer composition mayresolidify upon cooling to less than the melting temperature. Thisbehavior differs from the behavior of conventional elastomers, such asrubber.

The non-crosslinked block copolymer may function as a thermoplasticelastomer, improving the elasticity of the block copolymer proppantcoating. In embodiments, the crosslinked block copolymer may function asa thermoset elastomer. In embodiments, the crosslinked block copolymermay include thermoreversible crosslinking.

In embodiments where block copolymer is not crosslinked, the blockcopolymer composition may melt at a specific temperature range, known asthe melting temperature, resulting in a flowable medium. The blockcopolymer composition may resolidify upon cooling to less than themelting temperature.

In embodiments where the crosslinked block copolymer includesthermoreversible crosslinking, the crosslinks may reverse at the meltingtemperature, resulting in a flowable medium. The crosslinks may reformupon cooling to less than the melting temperature, such that the blockcopolymer composition may resolidify upon cooling to less than themelting temperature, and is once again crosslinked.

This cyclic process may be repeated an unlimited number of times,meaning that the block copolymer proppant coating may serve as a solidproppant coating at temperatures less than the melting temperature.Furthermore, this means the block copolymer proppant coating may meltwhen temperature increases to at or greater than the meltingtemperature, and may return to a solid block copolymer proppant coatingwhen the temperature decreases to less than the melting temperature.This behavior differs from the behavior of conventional thermosetrubbers. Conventional thermoset rubbers are single phase materials withnon-reversible chemical bonds which cannot be molten or melt-processed.

The crosslinked block copolymer may demonstrate rubbery elasticity, butmay not undergo plastic deformation due to the matrix structure of thecrosslinked block copolymer. Furthermore, the crosslinked blockcopolymer may be a thermoplastic elastomer, and therefore may not meltat temperatures of at least 100° C., of at least 150° C., of at least200° C., of at least 250° C., of at least 300° C., of at least 350° C.,or of at least 400° C. Without being bound by theory, the crosslinkedblock copolymer may not dissolve if exposed to hydrocarbons oraqueous-based solutions. Rather, the crosslinked block copolymer mayswell by from 0.5 to 6 wt. %, from 0.5 to 5 wt. %, from 0.5 to 4.5 wt.%, from 0.5 to 4 wt. %, from 0.5 to 3.5 wt. %, from 0.5 to 3 wt. %, from0.5 to 2.5 wt. %, from 2 to 6 wt. %, from 2 to 5 wt. %, from 2 to 4.5wt. %, from 2 to 4 wt. %, from 2 to 3.5 wt. %, from 2 to 3 wt. %, from 2to 2.5 wt. %, from 2.5 to 6 wt. %, from 2.5 to 5 wt. %, from 2.5 to 4.5wt. %, from 2.5 to 3 wt. %, from 3 to 6 wt. %, from 3 to 5 wt. %, from 3to 4.5 wt. %, from 3 to 4 wt. %, from 3 to 3.5 wt. %, from 3.5 to 6 wt.%, from 3.5 to 5 wt. %, from 3.5 to 4.5 wt. %, from 3.5 to 4 wt. %, from4 to 6 wt. %, from 4 to 5 wt. %, from 4 to 4.5 wt. %, from 4 to 6 wt. %,from 4.5 to 5 wt. %, or from 5 to 6 wt. % if exposed to hydrocarbons.

The block copolymer functions as a thermoplastic elastomer because thehard segments and the soft segments have different glass transitiontemperatures. As used in the present application, “segments” and“blocks” are used interchangeably. Glass transition is the gradual andreversible transition in amorphous materials (or in amorphous regionswithin semicrystalline materials), from a hard and relatively brittle“glassy” state into a viscous or rubbery state as temperature isincreased. The glass-transition temperature, T_(g), of a materialcharacterizes the range of temperatures over which this glass transitionoccurs. The glass-transition temperature of a homopolymer material (thatis, a consisting of identical monomer units) is less than the meltingtemperature, T_(m), of the crystalline state of the homopolymermaterial.

The soft segment has a glass transition temperature less than the glasstransition temperature of the hard segments. In many cases, ahomopolymer including the soft segment has a T_(g) of less than 20° C.,and the hard segments have a T_(g) of at least 80° C., of at least 90°C., of at least 100° C., of at least 150° C., of at least 200° C., of atleast 250° C., of at least 300° C., of at least 350° C., or of at least400° C.

In many cases, a homopolymer including the hard segments may have aT_(g) of from 80° C. to 400° C., from 80° C. to 350° C., from 80° C. to300° C., from 80° C. to 250° C., from 80° C. to 200° C., from 80° C. to150° C., from 80° C. to 100° C., from 80° C. to 90° C., from 90° C. to400° C., from 90° C. to 350° C., from 90° C. to 300° C., from 90° C. to250° C., from 90° C. to 200° C., from 90° C. to 150° C., from 90° C. to100° C., from 100° C. to 400° C., from 100° C. to 350° C., from 100° C.to 300° C., from 100° C. to 250° C., from 100° C. to 200° C., from 100°C. to 150° C., from 150° C. to 400° C., from 150° C. to 350° C., from150° C. to 300° C., from 150° C. to 250° C., from 150° C. to 200° C.,from 200° C. to 400° C., from 200° C. to 350° C., from 200° C. to 300°C., from 200° C. to 250° C., from 250° C. to 400° C., from 250° C. to350° C., from 250° C. to 300° C., from 300° C. to 400° C., from 300° C.to 350° C., or from 350° C. to 400° C.

Furthermore, the hard segments may comprise at least one aromaticmoiety. Specifically, the hard segments may comprise the polymerizedproduct of at least one monomer selected from styrene, alpha-methylstyrene, methacrylate, polyamide, and polyamine.

As used in the present application, the block copolymer is a polymerhaving at least two compositionally distinct subunits (A and B) derivedfrom different monomer species. In one or more embodiment, thesesegments may comprise oligomers or homopolymers. In another embodiment,a block copolymer may have at least three different subunits, A, B, andC in the block copolymer backbone. As used in the present application,“segments” and “blocks” may occasionally be used interchangeably as“sub-units”, but not in most instances. For example, a block copolymermay have an A-B-A structure, which means there only two compositionallydistinct sub-units A and B; however, there are three segments of thepolymer backbone with two of the three segments (such as the A segments)having the same composition (a triblock copolymer). As noted previously,in some embodiments, the block copolymer composition comprises at leastone anhydride group grafted onto the block copolymer backbone. Infurther embodiments, these anhydrides may be crosslinked by anamine-containing crosslinker.

The block copolymer composition includes at least one copolymerbackbone. Each copolymer backbone comprises at least two hard segmentsand a soft segment. The hard segments may be the end blocks of the blockcopolymer. Alternatively, the copolymer backbone may comprise more thanone soft segment, and these soft segments may be the end blocks of theblock copolymer. In some embodiments, the block copolymer has at leasttwo hard segments and at least one soft segment, where one of the atleast one soft segments is disposed between two of the at least two hardsegments. In some embodiments, the two hard segments are disposed as theend blocks of the block copolymer. In some embodiments, there are morethan one soft segments between the two hard segments disposed as the endblocks of the block copolymer. In some embodiments, only one of the twohard segments are disposed as the end block of the block copolymer. Insome embodiments, none of the hard segments are disposed as the endblocks of the block copolymer backbone. In some such embodiments, twosoft segments are disposed as the end blocks of the block copolymer.

As stated previously, each copolymer backbone comprises at least twohard segments and a soft segment. The soft segment is disposed betweenthe at least two hard segments. The soft segment may be aliphatic. Insome embodiments, the soft segment comprises the polymerized product ofone of more monomers selected from butene, butadiene, ethylene,tetrahydrofuran, ethylene oxide, propylene oxide, and acrylic acid. Thesoft segment may be unsaturated. The soft segment may have a glasstransition temperature of from −100° C. to −50° C., from −100° C. to−55° C., from −100° C. to −60° C., from −100° C. to −65° C., from −100°C. to −70° C., from −100° C. to −75° C., from −100° C. to −80° C., from−100° C. to −85° C., from −100° C. to −90° C., from −100° C. to −95° C.,from −95° C. to −80° C., from −95° C. to −85° C., from −95° C. to −90°C., from −90° C. to −80° C., from −90° C. to −85° C., from −80° C. to−50° C., from −80° C. to −55° C., from −80° C. to −60° C., from −80° C.to −65° C., from −80° C. to −70° C., from −80° C. to −75° C., from −75°C. to −50° C., from −75° C. to −55° C., from −75° C. to −60° C., from−75° C. to −65° C., from −75° C. to −70° C., from −70° C. to −50° C.,from −70° C. to −55° C., from −70° C. to −60° C., from −70° C. to −65°C., from −65° C. to −50° C., from −65° C. to −55° C., from −65° C. to−60° C., from −60° C. to −50° C., from −60° C. to −55° C., from −100° C.to 20° C., from −80° C. to 20° C., from −60° C. to 20° C., from −40° C.to 20° C., from −20° C. to 20° C., from 0° C. to 20° C., from 10° C. to20° C., from −100° C. to 10° C., from −80° C. to 10° C., from −60° C. to10° C., from −40° C. to 10° C., from −20° C. to 10° C., from 0° C. to10° C., from −100° C. to 0° C., from −80° C. to 0° C., from −60° C. to0° C., from −40° C. to 0° C., from −20° C. to 0° C., from −100° C. to−20° C., from −80° C. to −20° C., from −60° C. to −20° C., from −40° C.to −20° C., or from −60° C. to −40° C.

Furthermore, the copolymer backbone has at least one anhydride groupgrafted onto the soft segment. The anhydride group may be grafted ontoone of a secondary carbon or a tertiary carbon of the soft segment. Insome embodiments, the anhydride group comprises a succinic anhydridegroup, a maleic anhydride group, or combinations thereof. Specifically,the block copolymer having at least one anhydride group grafted onto thesoft segment may be a SEBS block copolymer and comprise this formula:

In some embodiments, the block copolymer may comprisestyrene-ethylene-butylene-styrene (SEBS) block copolymer, a lineartriblock copolymer including two styrene blocks and an ethylene/butyleneblock. The SEBS block copolymer may have a polystyrene content of from10 to 40 wt. %, from 10 to 35 wt. %, from 10 to 30 wt. %, from 10 to 25wt. %, from 10 to 20 wt. %, from 10 to 15 wt. %, from 13 to 40 wt. %,from 13 to 35 wt. %, from 13 to 30 wt. %, from 13 to 25 wt. %, from 13to 20 wt. %, from 13 to 15 wt. %, from 15 to 40 wt. %, from 15 to 35 wt.%, from 15 to 30 wt. %, from 15 to 25 wt. %, from 15 to 20 wt. %, from20 to 40 wt. %, from 20 to 35 wt. %, from 20 to 30 wt. %, from 20 to 25wt. %, from 25 to 40 wt. %, from 25 to 35 wt. %, from 25 to 30 wt. %,from 30 to 40 wt. %, from 30 to 35 wt. %, from 35 to 40 wt. %, of 30 wt.%, or of 13 wt. %. The SEBS block copolymer may have a specific gravityof from 0.8 to 0.95, from 0.8 to 0.9, from 0.85 to 0.95, from 0.85 to0.9, from 0.9 to 0.95, or of 0.91.

In other embodiments, the block copolymer may comprise polyether blockamide (PEBA) block copolymer. PEBA block copolymer is obtained bypolycondensation of a carboxylic acid polyamide with an alcoholtermination polyether, resulting in HO—(CO-PA-CO—O-PE-O)_(n)—H, where PAis a polyamide and PE is a polyether. PEBA block copolymer iscommercially available as VESTAMID, produced by Evonik Corporation.

The cement slurry may include from 0.1 to 10 wt. %, from 0.1 to 8 wt. %,from 0.1 to 7 wt. %, from 0.1 to 5 wt. %, from 0.1 to 3 wt. %, from 0.1to 2 wt. %, from 0.1 to 1 wt. %, from 0.1 to 0.5 wt. %, from 0.5 to 10wt. %, from 0.5 to 8 wt. %, from 0.5 to 7 wt. %, from 0.5 to 5 wt. %,from 0.5 to 3 wt. %, from 0.5 to 2 wt. %, from 0.5 to 1 wt. %, from 1 to10 wt. %, from 1 to 8 wt. %, from 1 to 7 wt. %, from 1 to 5 wt. %, from1 to 3 wt. %, from 1 to 2 wt. %, from 2 to 10 wt. %, from 2 to 8 wt. %,from 2 to 7 wt. %, from 2 to 5 wt. %, from 2 to 3 wt. %, from 3 to 10wt. %, from 3 to 8 wt. %, from 3 to 7 wt. %, from 3 to 5 wt. %, from 5to 10 wt. %, from 5 to 8 wt. %, from 5 to 7 wt. %, from 4 to 6 wt. %, or5 wt. % BWOC block copolymer composition. The cement slurry may include5.2 wt. % BWOC block copolymer composition.

The block copolymer composition may comprise from 0 to 10 wt. %, from 0to 5 wt. %, from 0 to 3 wt. %, from 0 to 2 wt. %, from 0 to 1.5 wt. %,from 0 to 1 wt. %, from 0 to 0.5 wt. %, from 0.5 to 10 wt. %, from 0.5to 5 wt. %, from 0.5 to 3 wt. %, from 0.5 to 2 wt. %, from 0.5 to 1.5wt. %, from 0.5 to 1 wt. %, from 1 to 10 wt. %, from 1 to 5 wt. %, from1 to 3 wt. %, from 1 to 2 wt. %, from 1 to 1.5 wt. %, from 1.5 to 10 wt.%, from 1.5 to 5 wt. %, from 1.5 to 3 wt. %, from 1.5 to 2 wt. %, from 2to 10 wt. %, from 2 to 5 wt. %, from 2 to 3 wt. %, from 3 to 10 wt. %,from 3 to 5 wt. %, or from 5 to 10 wt. % anhydride group. The blockcopolymer composition may comprise from 1.4 to 2 wt. % anhydride group.

Lastly, the copolymer backbone may be crosslinked. A crosslinker is asubstance or agent that induces the subsurface formation of crosslinks.Mixing a block copolymer with a crosslinker results in a chemicalreaction that crosslinks the block copolymer. Without intending to bebound by theory, crosslinking prevents the block copolymer from melting,and increases the elasticity of the block copolymer while retaining thebond between the block copolymer and cured cement. Specifically, theblock copolymer and the cured cement are bonded through both ionic bondsbetween the carboxylate groups of the block copolymer the calcium ionsof the cured cement, and covalent bonds between the hydrolyzed siloxygroup of the crosslinker and the hydroxyl groups of the silicates in thecement. In this way, the degree of crosslinking directly affects boththe internal structure and strength of the cured cement and the swellingcapabilities of the cement. The degree of crosslinking, reflected by theswelling values, can be controlled by the amount of the crosslinkeradded and the crosslinking duration and temperature. The degree ofcrosslinking provides a desired balance between the self-healing abilityand cyclic stress. In some embodiments, the crosslinker may comprisehexamethylenetetramine, paraformaldehyde, oxazolidines, melamine resins,aldehyde donors, resole polymers, aminosilane, or combinations of these.

In some embodiments, the crosslinker may be an aminosilane crosslinker.The aminosilane may comprise at least one of3-(2-aminoethylaminopropyl)trimethoxysilane and3-aminopropyltriethoxysilane. The block copolymer composition maycomprise from 0 to 5 wt. %, from 0 to 3 wt. %, from 0 to 2 wt. %, from 0to 1.5 wt. %, from 0 to 1 wt. %, from 0 to 0.5 wt. %, from 0.5 to 5 wt.%, from 0.5 to 3 wt. %, from 0.5 to 2 wt. %, from 0.5 to 1.5 wt. %, from0.5 to 1 wt. %, from 1 to 5 wt. %, from 1 to 3 wt. %, from 1 to 2 wt. %,from 1 to 1.5 wt. %, from 1.5 to 5 wt. %, from 1.5 to 3 wt. %, from 1.5to 2 wt. %, from 2 to 5 wt. %, from 2 to 3 wt. %, or from 3 to 5 wt. %aminosilane. The block copolymer composition may comprise 1 wt. %, 1.3wt. %, or 1.4 wt. % aminosilane.

The uncrosslinked block copolymer composition may have a meltingtemperature of from 150° C. to 250° C., from 150° C. to 240° C., from150° C. to 230° C., from 150° C. to 220° C., from 150° C. to 210° C.,from 170° C. to 250° C., from 170° C. to 240° C., from 170° C. to 230°C., from 170° C. to 220° C., from 170° C. to 210° C., from 180° C. to250° C., from 180° C. to 240° C., from 180° C. to 230° C., from 180° C.to 220° C., from 180° C. to 210° C., from 190° C. to 250° C., from 190°C. to 240° C., from 190° C. to 230° C., from 190° C. to 220° C., from190° C. to 210° C., from 200° C. to 250° C., from 200° C. to 240° C.,from 200° C. to 230° C., from 200° C. to 220° C., or from 200° C. to210° C.

The uncrosslinked block copolymer composition may have a melt flow indexof from 10 to 50 grams per 10 minutes (g/10 min), from 10 to 45 g/10min, from 10 to 40 g/10 min, from 10 to 35 g/10 min, from 10 to 30 g/10min, from 10 to 25 g/10 min, from 10 to 20 g/10 min, from 10 to 15 g/10min, from 15 to 50 g/10 min, from 15 to 45 g/10 min, from 15 to 40 g/10min, from 15 to 35 g/10 min, from 15 to 30 g/10 min, from 15 to 25 g/10min, from 15 to 20 g/10 min, from 20 to 50 g/10 min, from 20 to 45 g/10min, from 20 to 40 g/10 min, from 20 to 35 g/10 min, from 20 to 30 g/10min, from 20 to 25 g/10 min, from 25 to 50 g/10 min, from 25 to 45 g/10min, from 25 to 40 g/10 min, from 25 to 35 g/10 min, from 25 to 30 g/10min, from 30 to 50 g/10 min, from 30 to 45 g/10 min, from 30 to 40 g/10min, from 30 to 35 g/10 min, from 35 to 50 g/10 min, from 35 to 45 g/10min, from 35 to 40 g/10 min, from 40 to 50 g/10 min, from 40 to 45 g/10min, of 40 g/10 min, or of 22 g/10 min, measured at 230° C. by ASTMD1238.

The cement slurry may have a density of from 10 to 20 pounds per gallon(ppg), from 10 to 17 ppg, from 10 to 16 ppg, from 10 to 15 ppg, from 12to 20 ppg, from 12 to 17 ppg, from 12 to 16 ppg, from 12 to 15 ppg, from14 to 20 ppg, from 14 to 17 ppg, from 14 to 16 ppg, from 14 to 15 ppg,from 15 to 20 ppg, from 15 to 17 ppg, from 15 to 16 ppg, or of 15 ppg.

In some embodiments, the cement slurry may contain at least one additiveother than the block copolymer composition. The one or more additivesmay be any additives known to be suitable for cement slurries. Asnon-limiting examples, suitable additives may include accelerators,retarders, extenders, suspending agents, weighting agents, fluid losscontrol agents, lost circulation control agents, surfactants,antifoaming agents, and combinations of these. The suspending agents mayinclude at least one of a copolymer of N,N-dimethylacrylamide and sodium2-acrylamido-2-methyl propane sulfonate, and hydroxyethyl cellulose.

In some embodiments, the cement slurry may contain from 0.1 to 10% BWOCof the one or more additives based on the total weight of the cementslurry. For instance, the cement slurry may contain from 0.1 to 8% BWOCof the one or more additives, from 0.1 to 5% BWOC of the one or moreadditives, or from 0.1 to 3% BWOC of the one or more additives. Thecement slurry may contain from 1 to 10% BWOC of the one or moreadditives, from 1 to 8% BWOC, from 1 to 5% BWOC, or from 1 to 3% BWOC ofthe one or more additives. In some embodiments, the cement slurry maycontain from 3 to 5% BWOC, from 3 to 8% BWOC, from 3 to 10% BWOC, orfrom 5 to 10% BWOC of the one or more additives.

In some embodiments, the one or more additives may include a dispersantcontaining one or more anionic groups. For instance, the dispersant mayinclude synthetic sulfonated polymers, lignosulfonates with carboxylategroups, organic acids, hydroxylated sugars, or combinations of any ofthese. Without being bound by any particular theory, in someembodiments, the anionic groups on the dispersant may be adsorbed on thesurface of the cement particles to impart a negative charge to thecement slurry. The electrostatic repulsion of the negatively chargedcement particles may allow the cement slurry to be dispersed and morefluid-like, improving flowability. This may allow for one or more ofturbulence at lesser pump rates, reduction of friction pressure whenpumping, reduction of water content, and improvement of the performanceof fluid loss additives.

In some embodiments, the one or more additives may alternatively oradditionally include a fluid loss additive. In some embodiments, thecement fluid loss additive may include non-ionic cellulose derivatives.In some embodiments, the cement fluid loss additive may behydroxyethylcellulose (HEC). In other embodiments, the fluid lossadditive may be a non-ionic synthetic polymer (for example, polyvinylalcohol or polyethyleneimine). In some embodiments, the fluid lossadditive may include bentonite, which may additionally viscosify thecement slurry and may, in some embodiments, cause additional retardationeffects.

In some embodiments, the cement slurry may contain from 0.1% BWOC to 10%BWOC of one or more fluid loss additives, the one or more dispersants,or both. The cement slurry may contain from 0.02 to 90 pounds per barrel(lb/bbl) of the fluid loss additives, the one or more dispersants, orboth based on the total weight of the cement slurry. For instance, thecement slurry may contain from 0.1 to 90 lb/bbl, from 0.1 to 75 lb/bbl,from 0.1 to 50 lb/bbl, from 1 to 90 lb/bbl, from 1 to 50 lb/bbl, from 5to 90 lb/bbl, or from 5 to 50 lb/bbl of the fluid loss additives, theone or more dispersants, or both.

Embodiments of the disclosure also relate to methods of producing thecement slurries previously described. In some embodiments, the methodfor producing a cement slurry may include mixing water with a cementprecursor material and block copolymer composition produce a cementslurry. The water, cement precursor material, and block copolymercomposition may be in accordance with any of the embodiments previouslydescribed. The cement slurry may include one or more additives,including but not limited to defoamers, dispersants, and fluid lossadditives. The mixing step, in some embodiments, may involve shearingthe water, cement precursor material, block copolymer composition, and,optionally, other additives at a suitable speed for a suitable period oftime to form the cement slurry. In one embodiment, the mixing may bedone in the lab using a standard API blender for 15 seconds at 4,000rotations per minute (RPM) and 35 seconds at 12,000 RPM. The equation ofmixing energy is:

$\begin{matrix}{\frac{E}{M} = \frac{k\;\omega^{2}t}{V}} & {{EQUATION}\mspace{14mu} 1}\end{matrix}$whereE=Mixing energy (kiloJoules)M=Mass of slurry (kilograms)k=6.1×10⁻⁸ meters to the fifth power per second (constant foundexperimentally)ω=Rotational speed (radians/s)t=Mixing time (seconds)V=Slurry volume (cubic meters)

The method of producing the cement slurry may further includecrosslinking the block copolymer composition with an aminosilane aspreviously discussed. The block copolymer composition may be crosslinkedat a temperature of from 100° F. to 300° F., from 100° F. to 200° F.,from 100 to 150° F., from 100 to 180° F., from 150° F. to 200° F., from150° F. to 180° F., from 180° F. to 200° F., or at 180° F. Crosslinkingthe block copolymer composition may include rolling the block copolymercomposition in a roller oven for from 1 to 10 hours (hrs), from 1 to 8hrs, from 1 to 5 hrs, from 1 to 4 hrs, from 1 to 3 hrs, from 1 to 2 hrs,from 2 to 10 hrs, from 2 to 8 hrs, from 2 to 5 hrs, from 2 to 4 hrs,from 2 to 3 hrs, from 3 to 10 hrs, from 3 to 8 hrs, from 3 to 5 hrs,from 3 to 4 hrs, from 4 to 10 hrs, from 4 to 8 hrs, from 4 to 5 hrs,from 5 to 10 hrs, from 5 to 8 hrs, or from 8 to 10 hrs.

Further embodiments of the present disclosure relate to methods of usingthe cement slurries previously described. In some embodiments, themethod may include pumping the cement slurry into a location to becemented and curing the cement slurry by allowing the water and thecement precursor material to react. The location to be cemented may, forinstance, be a well, a wellbore, or an annulus.

Cementing is performed when the cement slurry is deployed into the wellvia pumps, displacing the drilling fluids still located within the welland replacing them with cement. The cement slurry flows to the bottom ofthe wellbore through the casing, which will eventually be the conduitthrough which the hydrocarbons flow to the surface. From there, thecement slurry fills in the space between the casing and the wellborewall, and hardens. This creates a seal so that outside materials cannotenter the well flow as well as permanently positions the casing inplace. In preparing a well for cementing it is important to establishthe amount of cement required for the job. This may be done by measuringthe diameter of the borehole along its depth using a caliper log.Utilizing both mechanical and sonic means, multi-finger caliper logsmeasure the diameter of the well at numerous locations simultaneously inorder to accommodate for irregularities in the wellbore diameter anddetermine the volume of the open hole.

In some embodiments, curing the cement slurry may refer to passivelyallowing time to pass under suitable conditions upon which the cementslurry may harden or cure through allowing one or more reactions betweenthe water and the cement precursor material. Suitable conditions may beany time, temperature, pressure, or humidity known in the cementindustry to cure a cement composition. In some embodiments, suitablecuring conditions may be ambient conditions. Curing may also involveactively hardening or curing the cement slurry by, for instance,introducing a curing agent to the cement slurry, providing heat or airto the cement slurry, manipulating the environmental conditions of thecement slurry to facilitate reactions between the water and the cementprecursor, or a combination of these. Usually, the cement will be curedand convert from slurry to solid due to subsurface formation conditions,temperature, and pressure. In the laboratory, a curing chamber capableof applying temperature and pressure is used for curing the cementspecimens at required conditions. Cylindrical molds (2 inch diameter and5 inch length) were lowered into the curing chamber. Pressures andtemperatures were maintained until shortly before the end of the curingwhere they were reduced to ambient conditions.

In some embodiments, curing may occur at a relative humidity of greaterthan or equal to 80% in the cement slurry and a temperature of greaterthan or equal to 50° F. for a time period of from 1 to 14 days. Curingmay occur at a relative humidity of from 80% to 100%, such as from 85%to 100%, or 90% to 100%, or from 95% to 100% relative humidity in thecement slurry. The cement slurry may be cured at temperatures of greaterthan or equal to 50° F., such as greater than or equal to 75° F.,greater than or equal to 80° F., greater than or equal to 100° F.,greater than or equal to 120° F., or greater than or equal to 180° F.The cement slurry may be cured at temperatures of from 50° F. to 250°F., or from 50° F. to 200° F., or from 50° F. to 150° F., or from 50° F.to 120° F., or from 50° F. to 180° F. In some instances, the temperaturemay be as great as 200° F., 300° F., 400° F., or 500° F. The cementslurry may be cured at pressures of greater than or equal to 20 poundsper square inch (psi), greater than or equal to 200 psi, greater than orequal to 500 psi, greater than or equal to 1000 psi, greater than orequal to 2000 psi, or greater than or equal to 3000 psi. The cementslurry may be cured at pressures of from 20 psi to 5000 psi, or from 200psi to 5000 psi, or from 200 psi to 3000 psi, or from 500 psi to 2000psi, or from 500 psi to 3000 psi. In some instances, the pressure may beas great as 1000 psi, 2000 psi, 3000 psi, 5000 psi, or 10000 psi. Thecement slurry may be cured for from 1 day to 14 days, such as from 3 to14 days, or from 5 to 14 days, or from 7 to 14 days, or from 1 to 4days, or from 4 to 7 days.

Further embodiments of the present disclosure relate to particularmethods of cementing a casing in a wellbore. The method may includepumping a cement slurry into an annulus between a casing and a wellboreand curing the cement slurry. The cement slurry may be in accordancewith any of the embodiments previously described. Likewise, curing thecement slurry may be in accordance with any of the embodimentspreviously described. As stated previously, cementing is performed whenthe cement slurry is deployed into the well via pumps, displacing thedrilling fluids still located within the well and replacing them withcement. The cement slurry flows to the bottom of the wellbore throughthe casing, which will eventually be the pipe through which thehydrocarbons flow to the surface. From there it fills in the spacebetween the casing and the actual wellbore, and hardens. This creates aseal so that outside materials cannot enter the well flow, as well aspermanently positions the casing in place.

Embodiments of the disclosure also relate to methods of producing curedcements. The method may include combining water with a cement precursormaterial and a block copolymer composition having at least one copolymerbackbone. Each copolymer backbone comprises at least two hard segmentsand a soft segment disposed between the at least two hard segments inwhich the copolymer backbone has at least one anhydride group graftedonto the soft segment, and in which the copolymer backbone iscrosslinked by an aminosilane crosslinker. The cement slurry may be inaccordance with any of the embodiments previously described. The methodmay include curing the cement slurry by allowing for a reaction betweenthe water and the cement precursor material to produce cured cement. Thecuring step may be in accordance with any of the embodiments previouslydescribed.

In some embodiments, cement is composed of four main components:tricalcium silicate (Ca₃O₅Si), which contributes to the early strengthdevelopment; dicalcium silicate (Ca₂SiO₄), which contributes to thefinal strength, tricalcium aluminate (Ca₃Al₂O₆), which contributes tothe early strength; and tetracalcium alumina ferrite. These phases aresometimes called alite and belite respectively. In addition, gypsum maybe added to control the setting time of cement.

Cement slurry design is based on altering the hydration reactions byadding or removing specific additives. In one embodiment, the silicatesphase in cement may be about 75-80 wt. % of the total material. Ca₃O₅Siis the major constituent, with concentration as great as 60-65 wt. %.The quantity of Ca₂SiO₄ conventionally does not exceed 20 wt. %, 30 wt.% or 40 wt. %. The hydration products for Ca₃O₅Si and Ca₂SiO₄ arecalcium silicate hydrate (Ca₂H₂O₅Si) and calcium hydroxide (Ca(OH)₂),also known as Portlandite. The calcium silicate hydrate commonly calledCSH gel has a variable C:S and H:S ratio depending on the temperature,calcium concentration in the aqueous phase, and the curing time. The CSHgel comprises +/−70 wt. % of fully hydrated Portland cement at ambientconditions and is considered the principal binder of hardened cement.Upon contact with water, the gypsum may partially dissolve, releasingcalcium and sulphate ions to react with the aluminate and hydroxyl ionsto form a calcium trisulphoaluminate hydrate (known as the mineralettringite (Ca₆Al₂(SO₄)₃(OH)₁₂.26H₂O)). The ettringite will precipitateonto the Ca₃O₅Si surfacesr, thereby preventing further rapid hydration.The gypsum is gradually consumed and the ettringite continues toprecipitate until the gypsum is consumed. The sulphates ionconcentration will decrease and the ettringite will become unstableconverting to calcium monosulphoaluminate hydrate (Ca₄Al₂O₆(SO₄).14H₂O).The remaining unhydrated Ca₃O₅Si will form calcium aluminate hydrate.

The cured cement may include one or more of calcium hydroxide,silicates, oxides, belite (Ca₂SiO₅), alite (Ca₃SiO₄), tricalciumaluminate (Ca₃Al₂O₆), tetracalcium aluminoferrite (Ca₄Al₂Fe₂O₁₀),brownmilleriate (4CaO.Al₂O₃—Fe₂O₃), gypsum (CaSO₄.2H₂O) sodium oxide,potassium oxide, limestone, lime (calcium oxide), hexavalent chromium,trivalent chromium, calcium aluminate, or combinations of these. Thecement precursor material may include Portland cement, siliceous flyash, calcareous fly ash, slag cement, silica fume, or combinations ofany of these.

The cured cement may exhibit self-healing characteristics. Specifically,the cured cement may swell in the presence of at least one of diesel,xylenes, aromatics, and chloroform, thereby self-healing any fracturespresent in the cured cement. The block copolymer composition of thecured cement may swell from 500% to 2000%, from 500% to 1600%, from 500%to 1500%, from 500% to 1100%, from 500% to 1000%, from 500% to 900%,from 500% to 700%, from 700% to 2000%, from 700% to 1600%, from 700% to1700%, from 700% to 1100%, from 700% to 1000%, from 700% to 900%, from900% to 2000%, from 900% to 1600%, from 900% to 1500%, from 900% to1100%, from 900% to 1000%, from 1000% to 2000%, from 1000% to 1600%,from 1000% to 1500%, from 1000% to 1100%, from 1100% to 2000%, from1100% to 1600%, from 1100% to 1500%, from 1500% to 2000%, from 1500% to1600%, or from 1600% to 2000%.

Compressive strength is the resistance of a material to breaking undercompression. A material with a greater compressive strength suffers lessfracturing at a given pressure as compared to a material with a lessercompressive strength. Greater compressive strength is desirable forcured cements in a wellbore, as the cured cement is less likely tofracture in downhole conditions, where pressure may be greater than 20psi, 200 psi, 500 psi, 1000 psi, 2000 psi, 3000 psi, 5000 psi, 7000 psi,or 10000 psi. The cured cement of the present disclosure may have acompressive strength of from 3500 to 6000 psi, from 3500 to 5500 psi,from 3500 to 5200 psi, from 3500 to 5000 psi, from 3500 to 4700 psi,from 3500 to 4500 psi, from 3500 to 4100 psi, from 4000 to 6000 psi,from 4000 to 5500 psi, from 4000 to 5200 psi, from 4000 to 5000 psi,from 4000 to 4700 psi, from 4000 to 4500 psi, from 4500 to 6000 psi,from 4500 to 5500 psi, from 4500 to 5200 psi, from 4500 to 5000 psi,from 4500 to 4700 psi, from 4700 to 6000 psi, from 4700 to 5500 psi,from 4700 to 5200 psi, from 4700 to 5000 psi, from 5000 to 6000 psi,from 5000 to 5500 psi, from 5000 to 5200 psi, or from 4000 to 5200 psi,meaning that the cured cement will not fracture until its compressivestrength has been exceeded.

Tensile strength is the resistance of a material to breaking undertension. A material with a greater tensile strength suffers lessfracturing at a given tension as compared to a material with a lessertensile strength. The cured cement of the present disclosure may have atensile strength of from 300 to 600 psi, from 300 to 550 psi, from 300to 525 psi, from 300 to 500 psi, from 300 to 450 psi, from 450 to 500psi, from 450 to 525 psi, from 480 to 520 psi, from 450 to 550 psi, from450 to 600 psi, from 500 to 525 psi, from 500 to 550 psi, from 500 to600 psi, from 525 to 550 psi, from 525 to 600 psi, or from 550 to 600psi, meaning that the cured cement will not fracture until its tensilestrength has been exceeded.

An elastic modulus measures a material's resistance to being deformedelastically, or non-permanently, when a stress is applied to it. Theelastic modulus of an object is defined as the slope of itsstress-strain curve in the elastic deformation region. A stiffermaterial will have a greater elastic modulus. The equation for anelastic modulus has the generic form:

$\begin{matrix}{\lambda = \frac{stress}{strain}} & {{EQUATION}\mspace{14mu} 2}\end{matrix}$where stress is the force causing the deformation divided by the area towhich the force is applied and strain is the ratio of the change in someparameter caused by the deformation to the original value of theparameter. The cured cement of the present disclosure may have anelastic modulus of from 1.5×10⁶ to 2.5×10⁶ psi, 1.5×10⁶ to 2.0×10⁶ psi,from 1.75×10⁶ to 2.5×10⁶ psi, from 1.75×10⁶ to 2.0×10⁶ psi, from1.75×10⁶ to 1.95×10⁶ psi, from 1.75×10⁶ to 1.9×10⁶ psi, from 1.75×10⁶ to1.85×10⁶ psi, from 1.85×10⁶ to 2.5×10⁶ psi, from 1.85×10⁶ to 2.0×10⁶psi, from 1.85×10⁶ to 1.95×10⁶ psi, from 1.85×10⁶ to 1.9×10⁶ psi, from1.9×10⁶ to 2.5×10⁶ psi, from 1.9×10⁶ to 2.0×10⁶ psi, or from 1.9×10⁶ to1.95×10⁶ psi.

In some embodiments, the cement slurry may contain water and may bewater-based. As such, the cement slurry may by hydrophilic, formingstronger bonds with water-wet surfaces. Well sections drilled withnon-aqueous drilling fluids may have oil-wet surfaces, resulting in poorbonding between the well and the cement slurry, as oil and waternaturally repel. Poor bonding may lead to poor isolation and a buildupof unwanted casing-casing or tubing-casing annular pressure. Withoutbeing bound by theory, it is desirable to make the subsurface formationor casing water wet to enhance and improve the bonding between cementand casing and cement and subsurface formation. If the wettability ofthe subsurface formation or casing is oil wet not water wet then thebonding will be poor and could result in small gap(s) or channel(s)between the cement and casing or the cement and subsurface formationthereby resulting in improper wellbore isolation. This improper wellboreisolation could lead to fluid or gas escaping from the well through thisgas or channel due to de-bonding.

EXAMPLES

The following examples illustrate features of the present disclosure butare not intended to limit the scope of the disclosure.

Example 1

In this study, two linear styrene-b-(ethyelene-co-butylene)-b-styrene(SEBS) block copolymers with succinic anhydride grafted onto the softsegment were crosslinked and added to cement compositions. The SEBSblock copolymers are commercially available from Kraton Corporation asKraton™ FG 1901 and Kraton™ FG 1924, the properties of which are listedin Table 1. These SEBS block copolymers contained polystyrene as thehard segment end blocks, ethylene/butene copolymer as the soft segment,and has been grafted with about 2 wt. % maleic anhydride. The catalytichydrogenation of maleic anhydride results in succinic anhydride. Astyrene-b-(ethylene-propene)-b-styrene block copolymer without maleicanhydride is available as experimental product Kraton™ MD 8703 (EDF10238). MD 8703 was used to evaluate the effect of the anhydride groupsin improving the mechanical properties of the cement. Theethylene-propene segment was derived by hydrogenation ofstyrene-isoprene-styrene block copolymer.

TABLE 1 Block copolymer properties. Property FG 1901 FG 1924Styrene/rubber (wt.%) 30/70 13/87 Relative Molecular Low Medium Weight(MW) -MW of each styrene  7500 13125 segment -MW of rubber segment 37500202000 Bound succinic 1.4-2.0    1 Anhydride (wt.%) Glass Transition −43.6   −40 Temperature, ° F. Melt Flow Index   22   40 (g/10 min) at230° C. (ASTM D1238) % Elongation at Break  500   750 Physical FormPowder Powder (Dusted with (Dusted with inorganic powder inorganicpowder to prevent particle to prevent particle adhesion) adhesion)Particle size D₅₀ - 410 μm; D₅₀ - 360 μm; D₁₀ - 276 μm; D₁₀ - 260 μm;D₉₀ - 1350 μm; D₉₀ - 510 μm Solid-Liquid Transition  215 TemperatureRange, ° F.

¹³C nuclear magnetic resonance (NMR) and ¹H NMR spectra of the threesamples clearly indicated that the spectral pattern of the aromaticregion of the spectra due the polystyrene segments was identical foreach of MD 8703, FG 1901, and FG 1924, indicating that the succinicanhydride group was grafted onto the soft segment, which indicatesregioselective substitution of the succinic anhydride group. Withoutintending to be limited by theory, it is believed that the succinicanhydride groups are chemoselectively substituted on secondary andtertiary carbons only. This is due to the abundance of methylene groupsand methane groups in middle segment (compared to the amount of methylgroups), and the stability of secondary and tertiary radicals during thefree radical initiated grafting of the succininic anhydride precursor(specifically, maleic anhydride).

The general structures of aminosilanes that are suitable forcrosslinking the SEBS block copolymer are shown in Formula 2 and Formula3. Specific examples of aminosilanes used in the study include3-(2-aminoethylaminopropyl)trimethoxysilane and3-aminopropyltriethoxysilane.NH₂—(CH₂)_(p)—SiR_(n)(OR¹)_(3-n)  Formula 2NH₂—(CH₂)_(m)—NH—(CH₂)_(o)—SiR_(n)(OR¹)_(3-n)  Formula 3

The crosslinking reactions were performed on 100 g each of FG 1901 andFG 1924 by dropwise addition of the aminosilane. The amounts ofaminosilane added are shown in Table 2. The crosslinked block copolymerswere then rolled in a roller oven maintained at 180° F. for 3-4 hrs toobtain the product as a loose particulate material. 1 wt. %3-(2-aminoethylaminopropyl)trimethoxysilane was added to FG 1901, whichresulted in the FG 1901 Modified 1 sample. 1 wt. %3-(2-aminoethylaminopropyl)trimethoxysilane was added to FG 1924, whichresulted in the FG 1924 Modified 2 sample. 1.4 wt. %3-aminopropyltriethoxysilane was added to FG 1924, which resulted in theFG 1924 Modified 3 sample.

TABLE 2 Amount of crosslinker added to each block copolymer.3-(2-aminoethyl- Block aminopropyl) 3-aminopropyl- Sample Name Copolymertrimethoxysilane triethoxysilane FG1901 - FG 1901 1 g/100 g block —Modified 1 copolymer FG 1924 - FG 1924 1.3g/100 g block — Modified 2copolymer FG 1924 - FG 1924 — 1.4 g/100 g block Modified 3 copolymer

After the crosslinking reactions were performed, the properties of themodified, crosslinked block copolymers were determined. These propertiesare shown in comparison to the original block copolymers in Table 3.

TABLE 3 Crosslinked block copolymer properties compared to originalblock copolymer properties. FG 1901 FG 1924 FG 1924 Property FG 1901Modified 1 FG 1924 Modified 2 Modified 3 Styrene/ 30/70 30/70 13/8713/87 13/87 rubber (wt.%) Relative Low Low Medium Medium MediumMolecular weight (MW) -MW of  7500  7500  13125  13125  13125 eachstyrene segment -MW of 37500 37500 202000 202000 202000 rubber segmentBound 1.4-2.0 <1.4-2.0 1 <1 <1 succinic Anhydride (wt.%) Glass  −43.6Not   −40 Not Not Transition measured measured measured Temperature, ° FMelt Flow   22 Not   40 Not Not Index (g/ measured measured measured 10min) at 230° C. (ASTM D1238) % Elongation  500 Not   750 Not Not atBreak measured measured measured Physical Powder Powder Powder PowderPowder Form (Dusted (dusting (Dusted (dusting (dusting with was with waswas inorganic retained inorganic retained retained powder from thepowder to from the from the to prevent parent prevent parent parentparticle sample) particle sample) sample) adhesion) adhesion) Particlesize D₅₀ - 410 D₅₀ - 376 D₅₀ - 360 D₅₀ - 880 D₅₀ - 280 μm; μm; μm; μm;μm; D₁₀ - 276 D₁₀ - 250 D₁₀ - 260 D₁₀ - 445 D₁₀ - <1 μm; μm; μm; μm; μm;D₉₀ - 1350 D₁₀ - 480 D₁₀ - 510 D₁₀ - 1765 D₁₀ - 420 μm μm μm μm μmSolid-Liquid  215 — — — — Transition Temperature Range, ° F.

Cement slurries comprising each of the samples were then preparedaccording to API Recommended procedures by adding blend of 713 grams APIClass G Portland cement, 37 grams (5.2% BWOC) of crosslinked blockcopolymer and 0.3 grams of a copolymer of N,N-dimethylacrylamide andsodium 2-acrylamido-2-methyl propane sulfonate to 324 milliLiters mixwater containing a defoamer.

A control slurry was prepared by mixing 713 grams API Class G Portlandcement, 37 grams MD 8703, and 1 gram hydroxyethyl cellulose with 400grams of water, cured and tested as described previously. A comparativeslurry with no block copolymer was also prepared by mixing 800 grams APIClass G Portland cement with 424 grams water and 1 gram hydroxyethylcellulose.

The block copolymer slurry densities were designed to have densities ofabout 15.0 ppg. The slurries were poured into 2″×5″ brass molds andcured at 180° F. under a pressure of 3000 psi for 4 days. The curingchamber was gradually depressurized after the heat was turned off. Thecement cylinders were trimmed to obtain 2″×4″ cylinders. The densitiesof the set cement samples containing block copolymers ranged from 14.6to 15.0 ppg with no density segregation, indicating no cement settlingor block copolymer separation.

Compressive strengths and elastic moduli were measured on the 2″×4″cement cylinders. Tensile strengths were measured using the splitcylinder method with 2″×1″ cement discs. The compressive strengths weremeasured by a Forney strength tester equipped with 250,000 pound loadcell. The rate of pressurization for the compressive strengthmeasurements was 266 pounds force per second (lb_(f)/s), and the rate ofpressurization for the split cylinder tensile strength measurements was33 lb_(f)/s. Self-healing of the cement compositions was measured bytesting the fractured cylinders and cylindrical discs from compressiveand tensile strength measurements. The cylinders and discs were wrappedindividually in aluminum foil, and clamped with C-Clamps or adjustablering clamps such that the fractured pieces were held together tightly.The cylinders and discs were placed in an oven at 200° F. for two days.The strength of adhesion was tested by manually attempting the breakthem apart for cylindrical discs and by measuring residual compressivestrengths for the cylinders. The cyclic stress measurements weremeasured by cutting 2 inch by 4 inch cylinders into two equalcylindrical halves, followed by measuring the compressive strength ofone cylinder, and using the strength values to set up the equipment forcyclic stress loading/unloading tests. The sample was subjected tocyclical stress loading and unloading between 90% and 20% of thecompressive values of the other half. The compression was increased by 5lb_(f) at the end of every cycle. The number of cycles the samplewithstood prior to failure was measured. The results are shown in Table4.

TABLE 4 Cured cement properties. Example Example Example EmbodimentEmbodiment Embodiment Comparative Cement with Comparative Cement withCement with MD 8703 Cement with FG 1901 Cement with FG 1924 FG 1924Property Control FG 1901 Modified 1 FG 1924 Modified 2 Modified 3Density 15.5 15 15 15 15 15 (ppg) Compressive 3750 4590 4685 3790 51904050 Strength, psi Tensile 240 420 500 400 505 500 Strength, psi Elastic1.88 × 10⁶ 1.74 × 10⁶ 1.95 × 10⁶ 1.59 × 10⁶ 1.85 × 10⁶ 1.87 × 10⁶modulus, psi Compressive Not 1500 400 1415 810 — strength of applicable(average of 2 (average of 2 (average of 2 (average of 2 self-healedsamples) samples) samples) Samples) samples, psi % Not 33% 9.0% 37% 16%— Compressive applicable strength retained after self- healing Number of1/3  1/1; 42/1  5/1; 260/1 437/1; Pressure 27/1 182/1 >618/1  cycles/(sample did Number of not break) samples tested

Table 4 shows that self-healing ability of cement composition issignificantly decreased when the succinic anhydride substituted blockcopolymers are crosslinked with aminosilanes. This is likely due to thecrosslinking preventing complete melting of the block copolymer, whichprevents the molten block copolymer from migrating into the fractures.However, the softening of the polystyrene phase to greater than theglass transition temperature allows the block copolymer to soften enoughto deform sufficient to partially bridge the fractured surfaces.

Surprisingly, the results in Table 4 indicate that the elastic modulus,compressive strengths and tensile strengths are increased in the exampleembodiment cement compositions as compared to the cement compositionsincluding non-crosslinked block copolymers. This is in contrast to theresults when using conventional elastomers, such as ground automobilerubber powders. These conventional elastomers cause a significantdecrease in compressive, tensile and flexural strength values, as wellas elastic modulus, in a cement composition.

Furthermore, the example embodiment cement compositions result in animproved cyclic stress resistance of the cement composition incomparison to the other samples. Therefore block copolymers comprisinghard end segments and soft middle segments with regioselective andchemoselective succinic anhydride groups will provide, upon crosslinkingwith aminosilanes prior to the addition of the block copolymer to cementcompositions, improved strength values and cyclic stress resistancewhile retaining self-healing properties both in the presence and in theabsence of swelling solvents.

Example 2

The swelling of the various block copolymer samples in various solutionsin shown in Table 5. The solutions were diesel, chloroform, xylenes andAromatic 200. Aromatic 200 was produced by CISCO Chemicals and includedfrom 50 to 85 wt. % C11 to C14 aromatic hydrocarbons, from 5 to 20 wt. %naphthalene, from 5 to 15 wt. % C10 aromatic hydrocarbons not includingnaphthalene, and from 5 to 15 wt. % C15 to C16 aromatic hydrocarbons.The swelling was measured by adding about 10 ml of solution to 0.26 gcrosslinked copolymer and storing the mixture at room temperature for aminimum of 4 hrs. The excess solvent was removed by decanting, and theswollen rubber solid was blotted with a paper towel and weighed. Theweight was divided by dry weight and multiplied by 100 to determine thepercentage of swelling. The tests including FG1901 Modified 1 and FG1924 Modified 2 in aromatic 200 solvent were not conducted, and the testincluding FG 1924 Modified 3 in xylenes solvent was not conducted. Theresults of the tests conducted are shown in Table 5.

TABLE 5 Block copolymer swelling and dissolving properties in varioussolvents. FG 1901 FG 1924 FG 1924 Solvent FG1901 Modified 1 F 1924Modified 2 Modified 3 Diesel Dissolves 680% Dissolves 1060%  1020% Xylenes Dissolves 700% Dissolves 930% Not determined Aromatic DissolvesNot Dissolves Not 825% 200 determined determined Chloroform Dissolves1040%  Dissolves 1570%  1460% 

The results in Table 5 show that the FG 1901 Modified 1 and FG 1924Modified 2 samples both swell in diesel, xylenes, and chloroform. The FG1924 Modified 3 sample swells in diesel, aromatic 200, and chloroform.Therefore, without intending to be bound by theory, it is likely thatcement compositions including these samples would also swell in thepresence of these solutions. Therefore, by injecting suitable solvents,with properties similar to the solutions used in this experiment, intofractures in cured cement, the fractures may be sealed effectively dueto expected swelling in the cement.

The following description of the embodiments is illustrative in natureand is in no way intended to be limiting it its application or use. Asused throughout this disclosure, the singular forms “a,” “an” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a” component includes aspects havingtwo or more such components, unless the context clearly indicatesotherwise.

It should be apparent to those skilled in the art that variousmodifications and variations may be made to the embodiments describedwithin without departing from the spirit and scope of the claimedsubject matter. Thus, it is intended that the specification cover themodifications and variations of the various embodiments described withinprovided such modification and variations come within the scope of theappended claims and their equivalents.

It is noted that one or more of the following claims utilize the term“where” as a transitional phrase. For the purposes of defining thepresent technology, it is noted that this term is introduced in theclaims as an open-ended transitional phrase that is used to introduce arecitation of a series of characteristics of the structure and should beinterpreted in like manner as the more commonly used open-ended preambleterm “comprising.”

Having described the subject matter of the present disclosure in detailand by reference to specific embodiments of any of these, it is notedthat the various details disclosed within should not be taken to implythat these details relate to elements that are essential components ofthe various embodiments described within, even in cases where aparticular element is illustrated in each of the drawings that accompanythe present description. Further, it should be apparent thatmodifications and variations are possible without departing from thescope of the present disclosure, including, but not limited to,embodiments defined in the appended claims. More specifically, althoughsome aspects of the present disclosure are identified as particularlyadvantageous, it is contemplated that the present disclosure is notnecessarily limited to these aspects.

What is claimed is:
 1. A method of cementing a casing in a wellbore, themethod comprising: pumping a cement slurry into an annulus between thecasing and the wellbore, where the cement slurry comprises: water, acement precursor material, and a block copolymer composition having atleast one copolymer backbone, each copolymer backbone comprising atleast two hard segments, and a soft segment disposed between the atleast two hard segments, in which the copolymer backbone has at leastone anhydride group grafted onto the soft segment, and in which theanhydride group is crosslinked by an aminosilane crosslinker; and curingthe cement slurry to cement the casing in the wellbore.
 2. The method ofclaim 1, in which the hard segments comprise at least one aromaticmoiety.
 3. The method of claim 1, in which the hard segments comprisethe polymerized product of at least one monomer selected from styrene,alpha-methyl styrene, methacrylate, polyamide, and polyamine.
 4. Themethod of claim 1, in which the hard segments are end blocks.
 5. Themethod of claim 1, in which the soft segment is aliphatic.
 6. The methodof claim 1, in which the soft segment comprises the polymerized productof one of more monomers selected from butene, ethylene, ethylene oxide,propylene oxide, and acrylic acid.
 7. The method of claim 1, in whichthe soft segment is unsaturated.
 8. The method of claim 1, in which theblock copolymer having the grafted anhydride group comprises the formula


9. The method of claim 1, in which the block copolymer comprisesstyrene-ethylene-butylene-styrene (SEBS) block copolymer.
 10. The methodof claim 1, in which the block copolymer has an A-B-A structure, inwhich A and B are two compositionally distinct sub-units.
 11. The methodof claim 1, in which the anhydride group comprises a succinic anhydridegroup, a maleic anhydride group, or combinations of these.
 12. Themethod of claim 1, in which the anhydride group is grafted onto one of asecondary carbon or a tertiary carbon of the soft segment.
 13. Themethod of claim 1, in which the aminosilane comprises3-(2-aminoethylaminopropyl)trimethoxysilane,3-aminopropyltriethoxysilane, or combinations of these.
 14. The methodof claim 1, in which the block copolymer composition comprises from 0.5to 2 wt. % crosslinker and from 1.4 to 2 wt. % anhydride group.
 15. Themethod of claim 1, in which the cement slurry comprises from 3% to 7%block copolymer by weight of cement precursor (BWOC).
 16. The method ofclaim 1, in which the cement slurry has a compressive strength of from4000 to 5200 psi when cured.
 17. The method of claim 1, in which thecement slurry has an elastic modulus of from 1.5×10⁶ to 2.0×10⁶ psi whencured.
 18. The method of claim 1, in which the cement precursor materialcomprises one or more components selected from the group consisting ofcalcium hydroxide, silicates, belite (Ca₂SiO₅), alite (Ca₃SiO₄),tricalcium aluminate (Ca₃Al₂O₆), tetracalcium aluminoferrite(Ca₄Al₂Fe₂O₁₀), brownmillerite (4CaO.Al₂O₃.Fe₂O₃), gypsum (CaSO₄.2H₂O),sodium oxide, potassium oxide, limestone, lime (calcium oxide),hexavalent chromium, trivalent chromium, calcium aluminate, quartz, orcombinations of these.
 19. The method of claim 1, in which the cementslurry contains from 0.1 to 10 wt. % BWOC of one or more additivesselected from the group consisting of accelerators, retarders,extenders, suspending agents, weighting agents, fluid loss controlagents, lost circulation control agents, surfactants, antifoamingagents, or combinations of these.
 20. The method of claim 1, in whichthe cement precursor material comprises Portland cement precursor,siliceous fly ash, calcareous fly ash, slag cement, silica fume, quartz,or combinations of these.